Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint and idempotentHint, so the read-only nature is covered. The description adds value beyond the annotations by disclosing the preflight behavior that prevents payment during RPC outages and noting that return data includes raw units and decimals provenance, which is useful context not in the schema or annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tightly written sentences, with the core behavior front-loaded and the preflight guarantee earning its place. There is no filler or repetition of schema content.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple read-only tool with two parameters, full schema coverage, and an output schema, the description covers the essential behavior, defaults, and a notable operational guarantee. Nothing an agent needs to invoke it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents both address and token_address. The description adds minor context (native ETH plus token, Base default, raw units) but does not materially expand on the parameter semantics beyond what the schema provides.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific operation (on-chain balance snapshot) with explicit scope: native ETH plus one ERC-20 token, defaulting to USDC on Base. This clearly differentiates it from sibling erc20_balance, which likely covers only token balances, and from other validation/check tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description makes the use case clear: when an EVM address's native ETH balance plus an optional ERC-20 token balance is needed, with a specific default token and chain. It does not explicitly name alternatives or exclusion conditions, so it stops short of a 5, but the context is strong enough for an agent to select it correctly.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.